For the final processing of spectacle glasses, the unfinished spectacle glasses, which are usually still round, and which already have the complete range of optical functions, are adapted to the spectacle frame and the individual characteristic values of the respective wearer (e.g. distance between the eyes). For this purpose, the unfinished lens, which is tensioned in the machine for edge processing, known as the “edger” can be calibrated. Then, the unfinished lens is machined to the contour of the end form with an over measurement. A measurement is again conducted in which primarily the position of the edges is to be determined, in order to incorporate corresponding form elements such as facets or grooves into the edge. In practise, sensing systems are usually currently used for measuring the lens, which measure the front and rear side of the lens until close to the edge. The disadvantage of the sensing systems is the risk of damaging the spectacle lens.
A method is already known from EP 1 250 979 B1, in which a laser beam is projected onto the edge of the lens and by means of a camera which stands at a fixed angle to the laser beam, the reflection is recorded and evaluated with regard to the radius and the height information of the edges. The disadvantage is the strong dependence on the surface quality or surface roughness of the unfinished spectacle lens which according to the principle in this document is subject to narrow tolerances. Furthermore, this type of measurement is affected by humidity on the lens. Finished lenses cannot be measured using such a method due to a lack of surface roughness.
DE 8715619 U1 describes the measurement of a spectacle frame with two laser micrometers which are arranged at right-angles to each other. It is mentioned that edges are measured, although on the basis of the description, it is clear that not the edges, but the expansion of the frame is determined, wherein an outer point of the frame does not always have to coincide with an edge.
A similar principle is described in DE 38 27 122 C2, according to which it is not the edge of the spectacle frame, but the radial expansion of the lens which is determined, which as can be seen with the example of a convex edge, does not always have to coincide with the edge.